Congers and morays (4)
I believe the answer is:
eels
'congers and morays' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eels that I've seen before include "Odd fish found in the lees" , "Devious types" , "Slippery customers" , "Fish (that may be jellied)" , "Else they're fish" .)